Christopher Monesky says it used to be service that dictated which airline he chose to fly. But now, it's all about the seat.

"I will not fly over five hours without lie-flat seating," says Monesky, a revenue manager in the hospitality industry who lives in Atlanta. "I (used) to be content with business-class recliners, but the times have gotten me so spoiled ... I cannot sleep on an overnight (or) long haul flight unless I am at 180 degrees."

First class on board a United Airlines 747. Photo: AP

He's not alone. Many corporate trekkers sing the praises of lie-flat seats, a perk that most large international carriers now offer on certain long-haul routes, such as those spanning the Atlantic or ferrying fliers cross-country, from New York to San Francisco.

"Without a doubt it is worth every penny to ensure that I am rested and prepared when I arrive at my international destination," says Sue Hershkowitz-Coore, a sales trainer and author who lives in Scottsdale, Ariz.

But those premium cabin perches don't come cheap. A business- or first-class seat on a cross-country or overseas flight can cost thousands of dollars. And upgrades sometimes require cash, as well as frequent-flyer miles.

For instance, the cost for a one-way upgrade to business class on a domestic Qantas flight from Melbourne to Perth ranges from 10,000 points for those who've paid a full economy fare to 16,000 points for those who have booked a discount economy ticket. Similarly on Virgin Australia, you'll need to cash in about 9900 points for an upgrade on a Sydney-Perth flight.

An upgrade on an international long-haul flight is typically a lot more. Upgrading to business class from economy on a Qantas flight from Sydney to Los Angeles will set you back 72,000 points.

To decide whether it's worth the extra cash or frequent flyer miles to grab a lie-flat seat, Bryan Saltzburg, general manager for TripAdvisor Flights and the air travel advice site SeatGuru, suggests having a checklist.

"I have a list of questions I'd ask myself," says Saltzburg. Among the points to tick off: Does the seat actually lie flat or is it at an angle? Do you really need to sleep during your trip? Would an economy seat with extra leg room suffice?

Typically, Saltzburg says, a traveller may want to spend the money for a lie-flat seat to sleep on a long-haul overnight flight to Europe, Asia or the US - but not for a daytime flight on the way back, when the sun is beaming through the cabin windows.

Or, he says, it could be worth the extra cost if a traveller decides "I have to be at work the next day. ... I need to be fresh at work."

For corporate trekkers who cannot justify spending several thousand dollars on a business-class seat, they might be able to purchase a less-expensive upgrade, if there's space, on the day of their flight. Or, he says, frequent flyers can use upgrade certificates or points to move up.

NUANCES OF ANGLES

Premium-class airline seats have been reclining more and more, as airlines use luxury perks to compete for business travellers who often book pricier, last-minute flights.

Cradle seats that resemble a living room recliner are being phased out, as are the angled flat seats that recline much further but still don't get down to 180 degrees, Saltzburg says.

"We're seeing a migration away from those seats to fully flat seats ... which are viewed as the most comfortable," he says.

Passengers who fly less frequently or usually sit in economy may not grasp the nuances that separate a recliner from a fully flat seat. But, Saltzburg says, "the experienced traveller understands the difference."

"I would take an extra stop in order to get onto an aircraft with a fully flat seat vs. a non-stop on a long flight ... where the seat wasn't fully flat," he says.

For the infrequent flyer, SeatGuru lets travellers see how different jetliners rank in overall comfort, including the type of seats on board the planes, their angle of recline, their space and size.

Many frequent business travellers have their own rules of thumb for when to purchase or use their points to upgrade to a seat that reclines so they can sleep.

David Bleser, a hotel industry consultant who lives in Austin, Texas, is a frequent flyer who makes his decision based on the numbers.

"How much is the upgrade? How long is the flight?" says Bleser, adding that he has to be in the air for at least three hours, and the upgrade can't be more than $200, for him to opt for a bed-like seat.

Brian McCarty, another frequent flyer, primarily uses his upgrades to grab a bed-like seat. But he only goes for the fully reclined seat on his longest trips, such as from the US to Australia, where he lives, versus a relatively shorter flight from Chicago to London.

"I do it because I get more done after the flight," says McCarty, a film sound engineer based in Cairns.

McCarty doesn't have trouble dozing in a coach seat, but says it's harder for his body to fully relax when it's virtually sitting upright during his in-fllight nap.

"After the lie-flat flights, I feel more refreshed and can more easily resume my activities despite the time-zone difference," he says.

He recently enjoyed the comfort of a lie-flat seat on a United flight from Chicago to Hong Kong. "Slept like a baby," he says.